drm/i915: Read C0DRB3/C1DRB3 as 16 bits again

We've defined C0DRB3/C1DRB3 as 16 bit registers, so access them
as such.

Fixes: 1c8242c3 ("drm/i915: Use unchecked writes for setting up the fences")
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210421153401.13847-3-ville.syrjala@linux.intel.com
(cherry picked from commit f765a5b4)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c

@@ -653,8 +653,8 @@ static void detect_bit_6_swizzle(struct i915_ggtt *ggtt)
 		 * banks of memory are paired and unswizzled on the
 		 * uneven portion, so leave that as unknown.
 		 */
-		if (intel_uncore_read(uncore, C0DRB3) ==
-		    intel_uncore_read(uncore, C1DRB3)) {
+		if (intel_uncore_read16(uncore, C0DRB3) ==
+		    intel_uncore_read16(uncore, C1DRB3)) {
 			swizzle_x = I915_BIT_6_SWIZZLE_9_10;
 			swizzle_y = I915_BIT_6_SWIZZLE_9;
 		}